Sir, my question to is that when DC current is applied through a capacitor with a bulb in a curcuit, why does the bulb stops glowing when capacitor is fully charged. If the DC power is exhausted then the charge stored in capacitor should make the bulb glow, but it didn't why is it so????????????and as according to video lecture when ac source is applied through a capacitor, the capacitor does not gets charged and it makes bulb glow for all the time,.... why is it so....I'm Confused ...pls help ????????????

Asked by PRIYANKAJ YADAV | 28th Oct, 2014, 09:51: PM

Expert Answer:

When DC is connected to capacitor with a bulb in a circuit, current will flow through circuit due to which capacitor will get charge. As charge accumulates on the capacitor plates, voltage across capacitor increases soon after battery voltage equals to voltage across capacitor. Therefore capacitor in a DC opposes the current as it charges. When the the capacitor is fully charged current in circuit falls to zero and the bulb stops glowing. 
when AC source is applied through a capacitor, It does not completely prevent the flow of charge. Capacitor gets charged and discharged alternately as current reverse in each half cycle of AC. The Capacitive reactance is given as Xc=1/omegaC. As C alpha 1/Xc .Hence on increasing value of C,value Xc decreases which makes bulb glow.

Answered by Priyanka Kumbhar | 29th Oct, 2014, 12:51: PM